I recently found this supplier. They are based in York and supply a reasonable range of Pololu and Sparkfun robotics parts, microcontrollers, sensors etc.
Prices are pretty reasonable, as is postage (free over £50). Delivery is lightning-fast, they give Farnell a run for their money!
Payment is via PayPal so you don't even have to trust them with your bank/card details (assuming you trust PayPal )
I have been getting my baby orangutan's from there.I have had 4 from them now.I used to get them from http://proto-pic.co.uk/,but after a few failiures,I changed to hobbytronics,and they appear to be very good.Next day delivery every time,so far!
I give them a gadget rating of *****
Just found this ebay shop called BestValueZone who sell the cheaper motorgearboxes.
Although at £6.85 including p&p they are dearer than the cheapest I have found, they are in this country so no long delays or chance of taxes. http://www.ebay.co.uk/itm/200768437301? ... 1423.l2648
They also have a large range of other bit including tiny switches.
Ordered them yesterday afternoon expecting them to turn up some time next week(standard 1st class post - cheapest delivery they offer) and they arrived in the post this morning!